I have the Hanna.
I like to use the refractometer during the brewing process because it's quicker (smaller samples, don't have to wait while the sample cools, etc.)
I've seen Sean's spreadsheet and it works.
I just use the hydrometer for the FG reading because I always have!
Besides, then I can drink the hydrometer sample!
I have this one http://www.amazon.com/Hanna-Instruments-Digital-Refractometer-Analysis/dp/B002NX0WHI/ref=sr_1_2?ie=UTF8&qid=1356794437&sr=8-2&keywords=hanna+refractometer
Piece of cake to use during brew day to see how close I'm getting to OG. I used to use it a lot more than I do now though, I guess because my recipes and process have become pretty standardized over the last 2 years. Probably overkill, there are better things to spend your $166 on... I still go with a trusted hydrometer during fermentation though
I use it more for maple sapping / syrup season.... it's a breeze to carry in the sugar bush and spot check the trees... and you gotta get your syrup to 66 Brix in the boil house... now that's a time of year coming on soon here in upstate NY!